Bug reported and fix proposed by Aris Spathis.

* src/sort.c (merge_markmem): Mark heap-allocated temporary key values.
(tim_sort): Delay key function calls to after marking function has been
registered.
* test/src/fns-tests.el (fns-tests-sort-gc): New test.

* test/src/editfns-tests.el
(editfns-tests--before/after-change-functions): Fix whitespace.

For `en/decode-coding-string/region`, `after-change-functions`
were either not run at all, or run only after deleting the text
but not after inserting it.

* src/coding.c (decode_coding_object, encode_coding_object): Run the
after-change-functions after inserting the result.

* test/src/editfns-tests.el (sanity-check-change-functions-with-op):
New macro.
(sanity-check-change-functions-errors): New function.
(editfns-tests--before/after-change-functions): Use them to add
cases for `en/decode-coding-string/region`.

* test/src/search-tests.el (test-replace-match-modification-hooks):
Delete, this is testing a functionality we can't really support.

* test/src/comp-tests.el (comp-tests-tco, comp-tests-fw-prop-1)
(comp-tests-pure): Update out of date pass names.

* lisp/treesit.el (treesit--things-around): Remove function.
(treesit-forward-sexp):
(treesit-beginning-of-thing):
(treesit-end-of-thing):
(treesit-navigate-thing):
(treesit-thing-at-point):
(treesit-outline-search): Use public version of thing-functions.
(treesit--thing-prev):
(treesit--thing-next):
(treesit--thing-at):
(treesit--navigate-thing): Make public.

* test/src/treesit-tests.el (treesit--ert-test-defun-navigation): Use
public version of thing-functions.

* src/search.c (Freplace_match): For ordering of *-change-functions.

* test/src/editfns-tests.el
(editfns-tests--before/after-change-functions): New test.
(sanity-check--message, sanity-check-change-functions-error)
(sanity-check-change-functions-check-size)
(sanity-check-change-functions-before)
(sanity-check-change-functions-after): New functions.
(sanity-check--verbose, sanity-check-change-functions-beg)
(sanity-check-change-functions-end)
(sanity-check-change-functions-buffer-size)
(sanity-check-change-functions-errors): New vars.

Previously, a unibyte target buffer could be put in an incorrect state
if json-insert was used to insert non-ASCII characters.

* src/json.c (Fjson_insert): Simplify.  Don't attempt to decode the data
being inserted: it is guaranteed to be correct UTF-8 and is correct for
both unibyte and multibyte buffers.
* test/src/json-tests.el (json-serialize/roundtrip)
(json-serialize/roundtrip-scalars): Extend tests.

* test/src/json-tests.el (json-parse-string/object):
Duplicated object keys are now retained in alist and plist output.
* etc/NEWS: Mention it.

* src/json.c (json_parse_value): Generate a plain parse error.
* test/src/json-tests.el (json-parse-string/short): Adapt test.